In addition to a central role in metabolism, mitochondria play a critical role in apoptosis/programmed cell death. The mitochondrial intermembrane space is home to several apoptotic components that mediate the degradation of proteins (cytochrome c, Smac/DIABLO, HtrA2/OMI), DNA (apoptosis inducing factor (AIF), and Endonuclease G), and, from our current studies, RNA (PNPase). Many pro- and anti-apoptotic proteins of the Bcl-2/Bax family are targeted to the mitochondrial outer membrane. Additionally, proteins normally resident to other subcellular compartments, such as Nur77 and Mud /are also targeted to mitochondria during apoptosis. Resident proteins of the mitochondrion follow very specific pathways for import and assembly in the organelle. Presumably, these apoptotic proteins utilize specific pathways for biogenesis that are important for their highly regulated role in apoptosis. The goal of this proposal is to use a combined genetic and biochemical approach in isolated mitochondria, S. cerevisiae, cell culture, and animal models to characterize the biogenesis of the mitochondrial intermembrane space apoptotic proteins. The first objective of this proposal is to characterize the import pathway of representatives in the various categories, based on the target of degradation (ie., DNA, protein, or RNA), beginning with PNPase. The second objective is to investigate the assembly and release of PNPase from the intermembrane space. The final objective is to investigate the role of PNPase in maintaining respiration and its link to apoptosis because loss of PNPase disrupts oxidative phosphorylation and lowers the membrane potential. In contrast to previous studies that have focused primarily on the individual components, this proposal will focus specifically on the events related to the biogenesis of apoptotic proteins in the mitochondrial intermembrane space and thus provide novel insights into the role of this compartment in programmed cell death. We will determine if the different apoptotic proteins might share conserved biogenesis pathways, which could be an ideal target for the development of new approaches to modulate several apoptotic pathways at one time. This application has a broader impact in public health because the mitochondrial events linked to apoptosis contribute to cancer and neurodegenerative diseases.